Worksheet solutions for chapter: Sound for class 9 are provided below.
(1) Give an example to prove that sound can travel in water.
Fill a tub with water. Shake a bell inside the tub. Now put your ear at the surface of water and listen the sound of bell. Therefore, sound can travel in water.
(2) Write two characteristics of the sound.
Ans- (i) The number of oscillations per second is known as frequency of oscillations. Therefore, the number of compressions or rarefactions that crosses our ear per unit time is known as frequency of sound waves.
Its unit is hertz(Hz). It is usually represented by .
(ii)The maximum extent of a vibration from the point of equilibrium is known as amplitude of vibration. In other words, the maximum displacement of an object or a vibration is known as amplitude.
(4) Why megaphone is used to make announcement.
Ans- Megaphone has a tube followed by conical opening which reflects sounds in forward direction without spreading in all direction. So that people can hear loud and clear announcement. Therefore, megaphones are used to make announcement.
(5)How ultrasonic waves are useful in ‘echocardiology’?
Ans-In ‘echocardiography’ ultrasonic waves are made to reflect from various part of the heart and form an image of the heart which is useful for medical treatment. This technique is called ‘echocardiology’.
(6) A ship sends out ultrasound that returns from the seabed and is detected after 2 s. If the speed of ultrasound through seawater is 1200 m/s, what is the distance of the seabed from the ship?
Ans- Time taken by the ultrasound, t = 2 s
Speed of the ultrasound, v = 1200 m/s
Let the distance of the seabed from the ship = d m
2d = v t
( 2d=distance between ship to seabed + distance between seabed and ship)
2d = 1200 (2)
= 2400 metre
d = 1200 m
Hence, distance between seabed and ship is 1200 m.
(7) Write the difference between the infrasound and ultrasound.
|Low frequency sound||High frequency sound|
|Frequency below than 20 Hz||Frequency higher than 20 kHz|
|Rhinoceroses, whale and elephants can communicate in low frequency.||Produced by dolphins, bats, moths etc.|
(9) Write the name of three bones which amplified vibrations several times in the middle ear.
Ans- The three bones which amplified vibrations several times in the middle ear are
(ii) anvil and
(10) What is the minimum time interval between the original sound and the reflected one to hear echo?
Ans– 0.1 second is the minimum time interval between the original sound and the reflected one to hear echo.